In the field of pulp treatment using a gaseous reaction medium, bleaching is of particular interest. In the past few years, a bleaching process was developed using an ozone step in combination with an oxygen bleaching step. A particularly beneficial variant of this process is high-consistency ozone bleaching. Consequently, various different processes for treatment of pulps are previously known. One of these processes is described in U.S. Pat. No. 3,814,664 and U.S. Pat. No. 3,964,962 to Carlsmith. Other processes for ozone bleaching of pulp are disclosed in U.S. Pat. No. 4,278,496 and U.S. Pat. No. 4,279,694 to Fritzvold. In these processes, pulp is placed in a tower and permeated by a gaseous medium such as oxygen or ozone. These processes, however, have not received general acceptance, primarily due to the random and poor bleaching results achieved.
In an effort to improve the bleaching results, various tests were conducted using a horizontal dynamic reactor upstream of the static bleaching tower in order to achieve more thorough mixing of the pulp with the oxygen or ozone bleaching agent. Examples of this type of process are described in EP 0 106 460 and U.S. Pat. No. 5,174,861. These processes and devices, however, also did not provide satisfactory bleaching results. In particular, the above-noted processes result in non-homogenous bleaching of the pulp as reported in "Importance of Reactor Design in High Consistency Ozone Bleaching" by White, Gandek, Pikulin and Friend (79th Annual Meeting CPPA).